Thermal protective device for electronic devices



Nov. 21, 1950 A. P. BOCK 2,530,935

THERMAL PROTECTIVE DEVICE FOR ELECTRONIC DEVICES Filed March 15, 1945 INVENTOR ATTORNEY WITNESSES:

Patented Nov. 21, 1 950 THERMAL PROTECTIVE DEVICE FOR ELECTRONIC DEVICES Ashley P. Bock, Catonsville, Md., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application March 15, 1945, Serial N0. 582,880

Claims.

My invention relates to electrical discharge tubes and, in particular, relates to arrangements for protecting the anodes of such tubes from overheating.

Certain types of electrical discharge tubes well known in the art have anodes which must be protected from overheating due to the energy set free at their surfaces by impact of electrified particles constitutin the electrical discharge current passing through the tubes. As one, although by no means the only, instance of such tubes, high vacuum oscillation generators used in the field of radio have metallic anodes, frequently forming a portion of the wall of the tube, at which considerable heat is set free during the normal operation of the tubes. So great, in fact, is the amount of this heat that arrangements are usually made for artificially cooling such anodes by streams of some fluid such as air or water. The greater the load current passing through the tubes the greater the amount of heat set free at the anodes, and it thus happens that the overload on the power system supplied with energy by the tube will heat the anode to a dangerous or destructive temperature.

One expedient previously used in the art for preventing the overheating of the anodes in such circumstances is to provide a relay responsive to overcurrent in the line wire carrying current to the anode. However, such arrangements have not proved to be entirely reliable inasmuch as overheating of the anode even with a normal current may occur at times due to slackening of the flow of cooling fluid or other abnormal conditions.

In accordance with my invention, I provide an improved form of protection of electrical discharge tube anodes from overheating by providing a thermal responsive device, such as a bimetal, which is in good thermal contact with the anode itself, and which operates the tripping coil of a circuit breaker in the line supplying current to the anode whenever the temperature of the anode reaches the critical value to which the thermal responsive device is set to respond.

However, in the case of many electrical discharge tubes such, for example, as the radio oscillation generator previously mentioned, it is common practice to operate the anode at a very high electrical potential, such as thousands of volts, above the earth. On the other hand, the circuit breakers, controlling supply of current to the anodes, are more conveniently located in lines which are not far removed in electrical potential from the earth. A problem, therefore, arises in making possible the operation of a circuit breaker substantially at earth potential by the closure or opening of a pair of thermal responsive contacts which stand at a potential of thousands of volts different from the earth.

One object of my invention is, accordingly, to provide an arrangement in which a thermal responsive relay can energize the tripping coil of a circuit breaker which is separated in electrical potential from the thermal responsive relay by a relatively high electrical potential.

Another object of my invention is to provide an arrangement by which the closure of a pair of contacts may cause actuation of a mechanism which is separated by a very high electrical potential from said contacts.

Still another object of my invention is to provide an arrangement in which a thermal responsive contact may control the operation of a circuit breaker which is separated in electrical potential from it.

Other objects of my invention will become apparent upon reading the following description taken in connection with the drawing and in which:

Figure 1 Shows a modification of my invention in which a pair of thermostat contacts positioned in proximity to the anode of a high voltage oscillation generator controls a circuit breaker governing the flow of power in a low voltage circuit furnishing power through a rectifier to said oscillation generator, and

Fig. 2 shows a different modification by which a thermal responsive element positioned in proximity to the anode of a high frequency oscillation generator controls a circuit breaker in a circuit supplying low voltage alternating current to the rectifier which supplies plate current to said generator.

Referring in detail to Fig. 1, an electrical discharge tube l, which may, for example, be a high vacuum triode having an anode '2 constituting a portion of its wall, has a control electrode 3 and a cathode 4 of conventional type. For example, the cathode 4 may be of a U-shaped filament heated by current from the secondary winding 5 of a transformer supplied with current from a primary winding 6 connected to low voltage alternating current line I. The secondary winding 5 has its midpoint connected to ground and also connected through a resistor 8 shunted by a capacitor 9 and through a radio frequency inductor II to the control electrode 3. An inductor l2 magnetically coupled to the inductor II is shunted by a circuit containing a load l3 in series carries substantial current.

to ground by wayofsecondary winding transformer secondary winding 22 of which the midpoint is grounded. A primary winding 23- connected to any suitable source of alternating current through a circuit interrupter 24 supplies energy to the rectifier. The circuit elements so far mentioned are of the type conventional in radio frequency oscillation generators and their power supplies.

In order to open the circuit breaker 24 in response to any overheating of the anode 2', a pair of thermostatically controlled contacts 25 which i may, for example, be those of a snap-disc bimetal, such as is' well known, are positioned in good heat-responsive relation to the anode 2; example, one contact of the bimetal may be in direct physical contact with the anode 2. The bimetal contacts 25 are connected to each other through a pair of inductors 26, 2? and through a pair of windings 28, 29. A pair of capacitors 3!, 32 are connected in series: across the lines-respectivelyconnecting inductor with winding 28 U and inductor 2'!- with winding 2%, and the midpoint of the capacitors 3i and 32 is grounded. A primary winding 33- which if desired, be connected to the alternating source 2, (or alternatively to any other suitable alternating current source) supplies energy to the secondary winding 28. A winding 34 is similarly magnetically coupled to the winding 29 and is connected to the energizing coil of a relay 35 which controls a pair of normally open' contacts 36, 3"! which close only when the energizing coil of relay 35 The contacts 36, 3'! are connected to the tripping coil of the circuit breaker 24 and upon closure act to open to main contact of the latter and thereby deenergize the transformer'winding 23-which supplies current through the above-mentioned rectifier to the anode tube.

The inductors 25-, 2? and the capacitors Si, 32 act as a filter to prevent radio frequency currents from the anode 2 from flowing through the windings 28 and 29.

The mode of' operation of the above described system is as follows. With the circuit breaker 24 closed, current is supplied from the positive terminal ifi of the rectifier to the anode'Z of tube I flowing thence to tube 3 and cathode' l thereof The current then flows through ground-tothe neutral point of transformer winding'22'and thence back through'the rectifier. By reason or the mutual inductance between the inductors i i and E2; the tube I will act to generate alternating currents and to supply them to the load i3.

As longas the anode 2 does not attain a temperature to which the contacts 35' are regulated to'respond'by closure, the secondary'winding 28 is unable to cause any substantial current flow through the winding 29 and the remainder of the circuit connecting contacts 25. As a result, the winding 29 is unable to substantially energize the relay 35; the contacts 36, 37 thereof remain open circuited, and the trip coil of the circuit breaker 24 remains deenergized. When, however, the

:anode 2 rises sufficiently in temperature so that 4 the thermostatic element closes the contacts 25, current is able to flow from the secondary winding 28 through th winding 29 which latter induces current through secondary winding 34 sufiicient to actuate the relay 35 to close contacts 36, 31. Sufficient current then flows through the latter and the trip coil of circuit breaker 24 to open the circuit and stop the supply of energy through primary winding 23 to the rectifier. The

? tube 1 is thus immediately 'deenergized and remains so until an attendant closes the circuit breaker 24. The anode 2 is thus protected from destructive overheating.

Turning to the embodiment of my invention shown in Fig. 2, an electrical discharge tube I which may be of the type already described in connection with Fig. 1 is provided with radio circuit connections comprising elements 2 through :5 which are similar to those already described in Fig. 1, and which accordingly need no separate description here. Direct current potential is supplied to the anode 2 from the rectifier tubes i9, 2ideriving energy from transformer windings 22 and 23 and circuit breaker 24 which are similar to the corresponding elements already dcscribed'in Fig. l, and which are believed to need no separate description in connection with Fig. 2. However, the line connecting the positive terminal ESof the rectifier to the anode 2 differs from that described in connection with Fig. 1 in that the choke coil ll of Fig. 1 is replaced by a winding 4! which is closely coupled magnetically to second'winding 42. The end of winding 42 remote from tube 2 is connected to ground through a; capacitor NBA. The winding 42 is connected in series .vith a pair of thermal responsive contacts ZS and-a primary winding 43 to one half of the secondary winding which supplies heating current to'the cathode of the tube 21. A secondary winding 44 which is in good inductive relation with the primary winding 43 supplies current to a'i'elay 'sficontrolling normally open contacts 36, Eiinseries with the trip coil of the circuit breaker E4. The elements 35, 35 and 31 and the circuit embodying them is similar to that already described in connection with Fig. 1.

The contacts 2?. are in good thermal responsive relation; such as direct contact, with the anode Aslong' as the contacts 25 are open, no current flows through the winding 42 or the primary winding 43' through the local circuit in which they are serially connected with the winding 4! andone' half of the secondary winding which supplies" heating current to the cathode of rectifier 21. The secondary winding 44 thus imposes no voltage on the relay 35; the contacts 36-and 31 remain open, and the trip coil of' circuit breaker isdeenergized. The rectifiers i9 and 2| correspondingly supply direct current to the tube 5' through thewinding 4|, and the tube l oscillatesand'supplies energy to the load l3 in the same manner as has already been pointed out in connection with Fig. 1.

However, when the anode 2 overheats, the conacts EEclose and one half the secondary winding upplying heating current to the tube 2! sends -urrcnt through the windings 43, 42, closed conacts 25, winding l! and the midpoint of the econdary winding which heats the cathode of cctifier 22. The windings 4i and 42 are so prop'oi'tioned and arranged that the fiow of this circulatory current just mentioned produces opposing magnetic effects in the windings Hand 42 so that their impedance to the flow of this circulatory current is substantially nil. The flow of this circulatory current in primary winding 43 acts in secondary winding 45 to energize the winding of relay 35, thereby closing contacts 36, 3'! to energize the trip coil of circuit breaker 24. The opening of the circuit breaker 24 thereby interrupts all supply of energy through the rectifier tubes 19 and 2! to anode 2. The tube I thereafter remains deenergized until an attendant recloses the circuit breaker 24.

The Fig. 2 circuit just described is very economical of insulation, inasmuch as it makes use of the insulation of the transformer which must be provided to supply heating current to the cathodes of rectifiers l9 and 2| which are at a high potential relative to earth. The only additional insulation not present in a prior art rectifier and oscillator system is, in fact, that which must be provided by the windings 43 and 44 which constitute a simple low frequency transformer insulated in ways well known in the transformer art. Since the windings ii and 42 always stand at susbtantially the same electrical potential, no problem will arise in insulating them from each other.

I claim as my invention:

1. In combination with an electrical discharge device, a thermal responsive element in good thermal relation to an electrode thereof, said thermal responsive device having a pair of separable contacts, means for including said contacts in series with a first transformer winding and a second transformer winding in a closed circuit, a third transformer winding insulated from said first transformer winding and arranged to supply it with energy derived from an alternating current source, and a fourth transformer winding insulated from said second transformer winding in cooperative relation with said second transformer winding and energizing a load device.

2. In combination with an electrical discharge device and circuit connections therefor in which at least one electrode operates at a high electrical potential relative to the earth, a thermal responsive device in good thermal relation with said one electrode, a pair of separable contacts operated by said thermal responsive device connected in series with a first transformer winding and a second transformer winding in a closed circuit, a third transformer winding insulated from said first transformer winding for said high potential and arranged to supply it with energy derived from an alternating current source, and a fourth transformer winding inductively coupled with and insulated from said second transformer winding for said high potential and energizing a load device.

3. In combination with an electrical discharge device having an electrode and certain connections adapted to subject said electrode to a, high electrical potential relative to earth, a thermal responsive device having a pair of separable contacts in good thermal relation with said electrode, said separable contacts being connected in series with a first transformer winding and a second transformer winding, a third transformer winding energized with alternating current in inductive relation with said first transformer winding and insulated therefrom for said high potential, and a fourth transformer winding in inductive relation with said second transformer winding and insulated therefrom for said high potential, and circuit control means energized by said fourth transformer winding.

4. In combination with an electron tube having an anode and a cathode, a rectifier embodying at least one cathode and an anode, a first transformer having a secondary winding connected to supply heating current to the cathode of said rectifier, a first channel connecting a point on the first mentioned secondary winding to said anode through a first inductive winding, a second channel connecting another point on the first mentioned secondary winding to said anode through a second transformer primary winding and through a second inductance which is in close inductive relation with said first inductance and also through a pair of separable contacts, a thermal responsive element actuating said separable contacts and in good heat responsive relation to said anode, and a secondary winding for said second transformer connected to apparatus which is substantially at the potential of the first mentioned cathode.

5. In combination with an electron tube having an anode forming a portion of its wall and a cathode, a rectifier embodying at least one cathode and an anode, a first transformer having a secondary winding connected to supply heating current to the cathode of said rectifier, a first channel connecting a point on the first mentioned secondary winding to said anode through a first inductive winding, second channel connecting another point on the first mentioned secondary winding to said anode through a second transformer primary winding and through a second inductance which is in close inductive relation with said first inductance and also through a pair of separable contacts, a thermal responsive element actuating said separable contacts and in good heat responsive relation to said anode, and a secondary winding for said second transformer connected to apparatus which is substantially at the potential of the first mentioned cathode.

ASHLEY P. BOOK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,565,151 Housekeeper Dec. 8, 1925 1,873,837 Gebhard Aug. 23, 1932 1,906,013 Gebhard Mar. 7, 1933 1,997,579 Gebhard Apr. 16, 1935 2,079,636 Sharp May 11, 1937 2,166,685 Henderson et al. July 18, 1939 2,203,579 Randolf June 4, 1940 FOREIGN PATENTS Number Country Date 37,179 Netherlands Dec. 1'7, 1935 

